An important input for an elevator controller relates to the load, or number of passengers, in the elevator car. U.S Pat. No. 4,330,836 granted May 18, 1982 to A. J. Donofrio, et al., relates to elevator cab load measuring, and contains a discussion of the desirability of monitoring car load, and the enhancement of elevator control derived therefrom. In the system disclosed in this patent, the elevator car is mounted on the frame by means of a plurality of elastomeric damped mount assemblies. There are, for example, six of the mount assemblies, and two of them will be equipped with force transducers which measure the car load.
U.S. Pat. No. 4,899,852 granted Feb. 13, 1990, to us discloses an elevator car mounting assembly wherein the car is suspended on the frame by a plurality of pendulum rods, one at each corner of the car. This patent briefly alludes to a load weighing assembly which is included in the mounting assembly.
U.S. Pat. No. 3,323,606 granted Jun. 6, 1967 to W. J. Bruns, et al., discloses an elevator load weighing apparatus which is installed in the machine room of the building housing the elevator. The elevator rope drive and sheave assembly are mounted on a bedplate in the machine room. The bedplate is mounted for pivotal movement about substantially its vertical mid plane, and one side of the bedplate is connected to a pressure transducer which measures the pivotal movement of the bedplate, which is proportional to the load in the elevator cab. Load weighing of the cab is thus performed in the machine room of the elevator system. The load weighing system of the aforesaid Bruns, et al., patent requires a complex machine mounting assembly and is not readily amenable to retrofitting to existing equipment in service in the field.
U.S. Pat. No. 4,766,977 granted Aug. 30, 1988 to S. Yamasaki discloses a load weighing apparatus for an elevator which detects cab load by measuring the traction sheave shaft torque with magneto-strictive material which is mounted on the sheave shaft between the sheave and gear or brake. The magnetic permeability of the material varies with torsional stress and thus is indicative of the torque on the machine and thus the load in the cab. This type of apparatus involves the use of a specially formulated material positioned on the output shaft, and is not readily retrofittable onto existing equipment in the field.